Adhesion promoter for UV curable siloxane compositions and compositions containing same

Abstract

An adhesion promoter for use with ultraviolet radiation curable siloxane composition is made by combining an alkoxysilicon compound of the formula (RO).sub.3 Si--X--Si(OR).sub.3 and a compound capable of catalyzing the reaction between two alkoxy groups or an alkoxy group and a hydroxyl group. Ultraviolet radiation curable siloxane compositions with the improved adhesion are obtained by mixing the adhesion promoter with a mixture which has at least one ultraviolet radiation activatable siloxane polymer and a photoinitiator. These compositions can be used as optical fiber coatings, conformal coatings, and other coating application where adhesion to a substrate is important.

That which is claimed is: 
     
       1. A method of improving the adhesion of a ultraviolet radiation curable siloxane composition to a substrate consisting essentially of blending to form a mixture of an ultraviolet radiation curable siloxane composition and an adhesion promoter which is a combination consisting of (A) an alkoxysilicon compound having a general formula   (RO).sub.3 Si--X--Si(OR).sub.3        in which R is methyl or ethyl and X is a divalent radical selected from the group consisting of --(CH 2 ) n  -- where n has a value of from 1 to 10 inclusive and --O(R' 2  SiO) m  -- where each R' is independently selected from a group consisting of RO--, an aliphatic hydrocarbon radical, and an aromatic hydrocarbon radical, where m has a value of from 0 to 20 inclusive, and   (B) a compound capable of catalyzing a reaction between two .tbd.SiOR groups in the presence of atmospheric moisture or between .tbd.SiOR and a hydroxyl group on a substrate,     applying the resulting mixture to a substrate, and then   exposing the resulting product to sufficient ultraviolet radiation to cure the mixture.   
     
     
       2. The method according to claim 1 in which (A) is ##STR22## 
     
     
       3. The method according to claim 1 in which (B) is an organotitanate. 
     
     
       4. The method according to claim 3 in which the organotitanate is tetrabutyltitanate. 
     
     
       5. The method according to claim 1 in which (A) is present in an amount of from 15 to 98 weight percent and (B) is present in an amount of from 2 to 85 weight percent wherein (A) plus (B) is 100 weight percent. 
     
     
       6. The method according to claim 2 in which (A) is present in an amount of from 15 to 98 weight percent and (B) is present in an amount of from 2 to 85 weight percent wherein (A) plus (B) is 100 weight percent. 
     
     
       7. The method according to claim 3 in which (A) is present in an amount of from 15 to 98 weight percent and (B) is present in an amount of from 2 to 85 weight percent wherein (A) plus (B) is 100 weight percent. 
     
     
       8. The method according to claim 4 in which (A) is present in an amount of from 15 to 98 weight percent and (B) is present in an amount of from 2 to 85 weight percent wherein (A) plus (B) is 100 weight percent.